The subject matter herein relates generally to isotope production systems and, more specifically, to components that have neutral particles incident thereon within an acceleration chamber of the isotope production system.
Radioisotopes (also called radionuclides) have several applications in medical therapy, imaging, and research, as well as other applications that are not medically related. Systems that produce radioisotopes typically include a particle accelerator, such as a cyclotron, that accelerates a beam of charged particles (e.g., H-ions) and directs the beam into a target material to generate the isotopes. The cyclotron includes an ion source that provides negative ions into an acceleration chamber of the cyclotron. The cyclotron uses electrical and magnetic fields to accelerate and guide the negative ions along a predetermined orbit within the acceleration chamber. The magnetic fields are provided by electromagnets and a magnet yoke that surrounds the acceleration chamber. The electrical fields are generated by a pair of radio frequency (RF) electrodes (or dees) that are located within the acceleration chamber. The RF electrodes are electrically coupled to an RF power generator that energizes the RF electrodes to provide the electrical field. The electrical and magnetic fields cause the negative ions to take a spiral-like orbit that has an increasing radius. When the negative ions reach an outer portion of the orbit, the negative ions are stripped of their electrons and form a particle beam that is directed toward the target material for isotope production.
As the negative ions are guided along the orbit, however, a portion of the negative ions may collide with other particles, such as residual gas molecules from the ion source. A negative ion may become a neutral particle upon colliding with the other particle. The neutral particle has a trajectory that is essentially tangent to the point in the orbit at which the negative ion collided with the other particle. The neutral particle then collides with other surfaces in the acceleration chamber, such as the RF electrodes. RF electrodes often comprise copper (or other conductive material). When a proton or a neutral hydrogen collides with copper, a relatively large amount of gamma and neutron radiation is generated and long-lived isotopes (e.g., Zn-65) may be generated. This is often the primary source of radiation within an acceleration chamber. Due to the geometry of the cyclotron in the acceleration chamber, the RF electrodes are particularly exposed to the neutral particles.
The accumulation of induced by-products from unwanted irradiation is a hazard to individuals. When service personnel open the acceleration chamber, the personnel are exposed to the activated parts. Moreover, the health risk created by the prompt radiation is often addressed by increasing the amount of shielding that surrounds the acceleration chamber. This can increase the cost of the cyclotron and require a larger space.